Multiple systems exist for distributing information about current events, like for example road hazards or natural disaster warnings. Such systems can be based e.g. on broadcasting technology. For example, the Traffic Message Channel (TMC) as part of the radio data system (RDS), using FM radio, is a common system for informing motorists about relevant events happening on the road.
Other systems, for example systems using mobile data connections of mobile telephone systems, don't use broadcasting, but unicasting to inform or warn user about events, like natural disasters.
Most events, like road hazard information or traffic warnings contain among others properties geographic information. This includes a geographic location or extent, describing where the event is happening, and also geographic information about the affected region. For example, a particular traffic jam might have a length, i.e. a geographic extent, of 2 km, and affects driving for 25 km behind the traffic jam on road M12.
Limiting the distribution of messages to a geographic location or extent is called geo targeting. In case of broadcasting the granularity, to which such geographic targeting can be performed, is dictated by the extent and organization of the broadcasting network. For example, the Austrian TMCplus FM radio traffic warning system uses three predefined broadcasting regions only for the whole of Austria, thus limiting geographic targeting of traffic event messages to selecting one or a combination of these three regions for broadcasting.
Another example for broadcasting would be using an enhanced Multimedia Broadcast-Multicast Service (eMBMS) system, as specified by ETSI and 3GPP (3rd Generation Partnership Project) TS 22.246, TS 23.246. eMBMS adds multicast and broadcast transmission modes to cellular networks. The smallest geographic region to which a broadcast or multicast can be targeted in eMBMS is called a service area (SA). A service area is made up from one or multiple nearby cells of a cellular network. Service areas can be grouped into broadcasting areas (BAs).
Due to the nature of broadcasting (a 1:n communication) the number of parallel receivers is theoretically unlimited, and in practice very high. On the other hand, receivers are not addressed individually, but all at once in a fixed, typically statically predefined, geographic area.
Geographic targeting in case of using unicasting (a 1:1 communication) requires that the sender is aware of the location of the receivers. The granularity of the geographic targeting is dictated by the granularity of the location information available to the sender. Once the sender knows the location of the receivers it can select only those located in an affected region and only unicast an event message to those receivers. This allows a dynamic geographic targeting per event message.
A very fine granularity for unicast event message distribution can be achieved by using Geo Location Messaging (GLM). With such a system the sender can be aware of any receiver's location with the same accuracy and precision the receiver is aware of its own position. E.g. receivers equipped with a global positioning system (GPS) know their location within a few meters, so the GLM sender does, too.
Geo Location Messaging uses unicast connections to send out event messages. At least one unicast connection is used for each receiver. If there are many receivers in the targeted geographic area this can lead to network congestion and the delayed reception of important messages, like a road hazard warning.
The geographic regions to which messages can be sent via broadcasting are fixed by the extent and organization of the broadcasting network. For example, in case of an eMBMS network, the region is fixed by the defined service areas. There is also the possibility that messages are received outside of a designated service area due to the propagation properties of RF signals. Control over the geographic region to which a particular event message is distributed is therefore limited.
Another problem is that when using multiple unrelated event message distribution systems in parallel, e.g. GLM and eMBMS, the duplicate delivery of event messages leads to wasting of network resources.